Burner control



Oct.25, 1938. J. EATON 2 ,134,550

BURNER CONTRIOL Fild July 14/ 1954 3 Sheets-Sheet 1 7 5 3 F J 2 W l 8/ T J 2 64 C a5 c I 52 0 5" 7 AZ A! 82 y Inventow: John Eaton,

His A'bt own egg.

1.938- v "J. EATON 2 1 5 BURNER CONTROL Filed July 1,4; 1934 s Sheets-Sheet 2 Invent ov--: I jiohn gat is Attorhe Oct 25, 1938.

J. EATON 2,134,550

BURNER CONTROL v Filed July 14, 1934 s S he ets-Sheet s Inventor i i 1313 orngg Patented Oct. 25, 1938 UNITED STATES BURNER CONTROL John Eaton, Schenectady, N. Y., assignorjto General Electric Company, a. corporation of New York application July 14, 1934, Serial No. 735,103

2Claims.

' The invention relates to automatic fuel burner control systems and apparatus such as used with oil fired boiler furnaces for heating homesor in other similar service. r 5 v The principal object is to provide improvements which insure the maximum safety in the automatic control and operation of the fuel burner as well as safe operation of the boiler furnace. A further object is to provide an improved form of boiler low water cutoff for preventing operation ofthe fuel burner in case the boiler water level falls below a predetermined safe value in a steam or vacuum vapor heating system. A still further object is to provide an improved form of combined room thermostat and limit control for effecting operation of the fuel burner in accordance with both room temperature and certain other conditions such as boiler temperature, domestic hot water temperature, steam pressure or the like. I

I Another important'object is to provide a fully automatic fuel burner control system and apparatus which falls safe by insuring against'con- -tinued operation of the burner in case of accidental failure or faulty operation of the im-.v

portant safety control elements, such as" the flame detector, the low water cutoff, the fuel supply control and the like. q

It is also a special object to provide an improved unitary structural arrangement for the automatic fuelburner and boiler control mechanism whereby reliability, ease of installation, in spection and adjustment of the various auto-' matic operating elements are obtained.

' A preferred form of automatic oil burner control system and apparatus embodying the improvements of .thepresent inyention is illustrated in theaccompanying drawings. Fig.1 is a schematic diagram showing the improved form of oil burner safety control system and apparatus applied to an electric motor driven, oil burner mechanism adapted for use in combination with a vacuum vapor house heating boiler; Fig. 2 is a sequence diagram indicating the predetermined timed relations in which the various op-- erations involved in starting the oil burner and establishing combustion are accomplished urider the control of a room thermostat, a boiler thermostat or similar master control element, by the improved safety control system and apparatus shown in Fig. 1; Fig. 3 shows more fully the cooperating arrangement and detailed structure of the various elements of the oil burner timing control mechanism and certain-of the safety energizing circuit.

1; Fig. 4 is a top view of the timing and safety control mechanism shown in Flg. 3; Fig. 5 is a sectional view of the improved low'water safety control element embodied in the oil burner control system of Fig. 1; Fig. 6.is a front view show- 5' ing the safety switch mechanism of the low water safety control element,.and Fig. '7 is a view of the top part of the oil burner boiler showing more clearly the manner in which the oil burner mechanism and timing and safety control 10 mechanism therefor is mounted on the boiler; To comply withthe requirement of the Patent Oflice, a divisional application, Serial No. 11,100, was filed March-14, 1935, with claims directed to the improved oil burner control system illus- 15 trated in Fig. 1, which divisional application was issued as Patent No. 2,085,577 on June 29, 1937.

As diagrammatically shown in Fig. 1 the boiler furnace I0 is of the improved type described and claimed in the copending application of 20 Henry S. Woodrufi', Serial No. 676,651, filed June 20, 1933;; and assigned to the assignee of my present invention. It'will .be understood, however, that the improvements 'of my present invention are applicable to control any ordinary 25 type of automatically fired boiler or furnace.

or absence of combustion. As indicated the flame vdetector I4 is of the expansible heat responsive type although any quick acting type of flame detector may be employed. I

An oil control valve 11 is shown incorporated 40 in the oil burner nozzle II for starting and stopping the supply of oil into the combustion chamber l3.- Oil valve I1 is normally closed and is opened only when theoil valve operating electromagnet, I8 is energized. As pointed out here- 45 after electromagnet Ills providedwith a holding circuit formaintaining valve il open after it is once opened independently of the initial As shown'*in Fig. 7 oil and. air are supplied under pressure to the burner 50 nozzle II from the electric motor operated oil burner blower compressor mechanism 20.

The oil atomizing nozzle ll and 'o'il valve l'l' preferably are of the type, described and claimed control elements'shown diagrammatically in Fig.

in my copending joint application, Serial No. 55

691,320, filed September 28, 1933, although the present invention is not limited thereto.

The oil burner motor compressor mechanism 20 preferably is of the type described and claimed in the copending application of Walter 0. Lum, Serial No. 737,063, filed July 26, 1934, and assigned to the assignee of my present invention. The oil burner mechanism 20 has an electric driving motor 2| which drives a suitable oil and air pumping means located inside of the tank 22 for pumping oil and air under pressure into the tank. The air under pressure is supplied from tank 22 directly to the burner nozzle through the pipe 23 and the oil under pressure is supplied to the nozzle upon opening of oil control valve l1 through the pipe 24. Low pressure combustion air is supplied from the blower 25. As indicated diagrammatically in Fig. 1 the oil burner motor 2| is provided with a running winding 21 and a starting winding 28.

The oil burner mechanism is operated under the control of the room thermostat 30 to heat the water in the boiler I!) to supply steam or vapor to a room heating radiator system (not shown). In addition the oil burner mechanism is also operated under the control of. the water thermostat 3|. As shown the water thermostat 3| is of the expansible bellows type having the bulb 32 responsive to the temperature of the water in the boiler Ill. The thermostat 3| serves to operate the oil burner mechanism to maintain the boiler water temperature above a predetermined value 'suflicient to heatan adequate supply of domestic hot water by means of the water heating coil 33 which is shown immersed in the boiler water.

A bellows 35 is responsive to the pressure in boiler l0 and serves to shut down the oil burner mechanism whenever an excessive pressure occurs. An improved form of electrically heated low water cutout switch mechanism 36 having a heater 34 is provided for preventing operation of the oil burner mechanism whenever the boiler water level falls to an unsafe value. The detailed construction of the low water cutoif mechanism quence of operation of the various elements com-'- prising the oil burner mechanism, a timing control device indicated generally by the reference numeral 40 is provided. In the preferred form indicated diagrammatically in Fig. 1 and shown more in structural detail in Figs. 3 and 4, a cam shaft 4| is driven by the electric timing motor 42 which preferably is of the alternating current constant speed type such as commonly used in electric clocks. The cam shaft ll carries aseries of timing cams indicatedrespectively as B F, 0 0 T, and I, all of'which are rotated in unison in a clockwise direction as indicated by the arrow in Fig. 1 upon operation of the timing motor 42. Each of these cams has a corresponding cam operated switch contact mechanism arranged so that a definite series of switching operation is performed in timed sequence in the manner described more fully hereinafter in connection with the operation.

Cooperating with the timing cam operated switch mechanism are a series of. electromagnetically operated switches indicated as A, B and C, each having a pair of circuit controlling switch contacts indicated respectively as A A B B and C C in Fig. 1. 1

As shown more in detail in Figs. 3 and 4, the cam shaft 4| is rotatably supported between the side plates 4,3 and 44 with the motor 42 driving thecam shaft through the speed reducing gearing 45. The series of spring contacts operated by the cams B F, 0 0 T and I are mounted between suitable blocks of insulating material 46 and 41. Likewise the spring switch contact mechanism of the electromagnetic switches A, B and C are mounted between blocks 41 and blocks 48, the operating electromagnets therefor being mounted below the contact mechanism as indicated in Fig. 3. The side plates 43 and M are secured to'a cover plate 50. As indicated in Fig. 3

plate 50 is arranged to cover an opening 5| provided in the top wall 52 of boiler l0, being removably bolted in place with suitable gasket to seal the boiler wall.

The cover plate 50 carries the boiler water thermostat 3|, the boiler pressure responsive bellows 35 and the vacuum relief valve 31', all as a unitary structure with the oil burner timing control mechanism 4|]. With this improved unitary arrangement, the expansible bellows thermostat 3| is connected through the overcenter snap action spring operating mechanism 55 to mechanically operate the contact switch mechanism A of the electromagnetic switch A. At the same time the thermostat 3| operates the vacuumrelief valve 31. Similarly the expansible bellows of the boiler pressure responsive device 35 operates the spring contact switch L through the agency of the overcenterspring snap action mechanism 56.

The operation of the improved burner control system and apparatus illustrated is as follows: When the room thermostatic switch 30 calls for heat, the running contact R is closed. When the room thermostat exceeds the temperature which it is adjusted to maintain the contact S is closed 1 to stop the oil burner. While not shown in detail it will be understood that the electricallydriven clock 51 serves to vary the setting of the room thermostat 30 to provide different day and night temperature in home heating service in the customary manner. When the room thermostat 30 closes the running contact R, the A electromagnetic switch or relay is energized. As shown in Fig. 1 the A relay is energized from the low voltage secondary winding of the control transformer CT having the primary winding thereof energized from a suitable alternating current power source L 1? with the contacts of the low water cutoff switch 36 and also the safety plug switch 58 connected in the primary circuit. The safety switch 58 is arranged to be opened by the pressure "relief door 59 in case an excessive pressure should develop within the combustion chamber. 3 -of the oil burner [0. Likewise the low water cutofl' switch 36 opens in case the water in boiler l0 reaches a dangerously low level, the precise manner in which the switch 38 isopened being described more fully hereinafter. However, upon ,the occurrence of either of these abnormal and unsafe conditions, the primary of the control transformer CT is deenergized thus effectively preventing further operation of the oil burner.

relay A to the terminal S of the transformer secondary winding. This results in operation of relay A to close both contacts A and contacts A. Contacts A shunt the roomthermostat contact R and connect the energizing winding of relay A directly to the terminals R and S of the transformer, thus maintaining relay A continuously energized independently of the room thermostat Upon closure of contacts A an energizing circuit for the operating winding of relay C is closed provided the movable contact ii of the flame detector I4 is in the cold position as indicated in Fig. l.

Normally the flame detector l4 operates its movable control contact l5 to the cold position quickly in response to the absence of combustion in the combustion chamber l3 of the boiler l0. Relay C is energized from the supply line L through conductor l, the normally closed contacts of the pressure limit switch L, conductor 2,

contacts A conductor v3, the'cold contacts of the flame detector l4, conductor 9, the winding of V relay C and thence to the supply line L.

Upon the resulting operation of ,relay C, contacts C and C are closed. Contact C establishes an energizing circuit for the timing motor 42.

This circuit is traced from conductor 3 which remains energized from the supply line I! as long as v the contacts A and the limit contacts Lremain closed, through contacts C and conductor",

' the energizing winding of timing motor 42 to the supply line L Thereupon the timing motor 4! begins to rotate the series of timing cams carried by the shaft 4|.

At the same time the opening of the normally closed contact C opens the holding circuit of the oil valve operating electromagnet l8, this circuit being traced from the supply line L through the safety door switch contact 58, .the low water cutoff switch 36, the conductor I, the limit switch L, the conductor 2, the contact A conductor 3, the contact B conductor 4, the normally closed contact C the electric heater 34 of the low water cutoff switch and thence through the energizing winding of the valve operating electromagnet Hi to the supply line L As will .be'pointed out hereinafter, this opening of the oil valve holding circuit is an important factor in insuring safe operation of the oil burnercontrol.

. As indicated in the sequence chart of Fig. 2, there is a considerable interval a of time afterthe starting of the timing motor 42 before the sequential operation of the timing cam switches begins. At the end of interval a the cam I closes its contacts to energize the primary winding of the ignition transformer IT, the circuit extending from the conductor 3 which remains energized as previously pointed out through the contacts of the cam switch I, the primary of the ignition transformer to the supply line 192- The cam contact I remains closed to maintain the spark l2 energized from the high ignition electrode voltage secondary winding of, the ignition transformer during almost the entire starting cycle of the oil burner. This insures that any oil supplied from the nozzle ll 'atany time during this cycle is'ignited. This insuresthat ignition is alend of the short limited interval 9.

ways present to ignite any oil delivered from the oil burner nozzle II at any time during the starting cycle.

After a relatively short time interval b, the

cam F operates to close its contact and establish a circuit for energizing the start winding of the oil burner moton. After a longer time interval 0,

cam B operates to close its contact. Thereupon an energizing circuit for the relay B is established. This circuit is traced from conductor 3 which remains energized from the supply line L as previously pointed out, through contact'C conductor I2, cam contact B and thence through conductor 13 and the energizing winding of the operating electromagnet of relay B. Relay B responds to close both of its contacts B B. Upon closure of contact B both the start and the run windings of the oil burner motor are energized. The circuit for the running winding is traced from the conductor 3 which. remains energized from supply line L under normal conditions through the cam contact 3 conductor 4 and thence through the run winding to supply line L. The energizing circuit of the start winding eigtends from conductor 4 through the previously closed cam contact F, conductor 5, and thence through the start winding to supply line 1?. The oil burner driving motor immediately starts operation of the oil and air pumping means to pump oil andair under pressure into thetank 22 and to supplyalr from the blower 25 to the combustion chamber l3 of the boiler. malconditions there is no oil supplied into the However, under norcombustion chamber due to the fact that the oil supply control valve I'I remains closed.

During the interval d the oil burner motor comes up to speed and operates with both the running and the starting winding energized. At

the end of interval C cam F opens its contact to 1 deenergize the starting winding and the oil burnor motor continues at full speed operation with the run winding. energized alone.

During the intervals (2 and e, the operation of the oil burner motor serves to build up full pressure of the oil and air in the tank 22, at the same time the ignition electrodes are in operation to provide a spark for igniting the 011. At the end of interval e,.the cam T closes its contact to maintain the timing motor 42 energized through a circuit which is independent of the initial energizing circuit established by closure of contact C as previously described. Upon closure of the cam contact T, the conductor 3 is connected directlythe cam contact T. All that remains to be done to establish com-" bustion conditions is to open the oil valve I! for a predetermined limited interval such that only a safe amount of unburned oil is projected into the combustion chamber l3 of the boiler I!) in case for some unknown reason there isfailure to establish combustion. The opening of the oil valve for this predetermined limited interval 9 is accomplished by the joint action of the two timing cams O 0*. Cam 0 serves to close the energizing circuit for the operating electromagnet l8 of the oil valve -at the endof interval 1 and cam 0 operates to open this circuit at the side.

This is accomplished in the following-manner: During the rotation of the cam shaft 4|, the cam O is moved into engagement with the spring contact 0 and the cam O is moved into engagement with the spring contact 0 Upon continued rotation of cam shaft 4| during the time preceding the end of interval f, cams O and O serve to move the spring contacts 0 and O downwardly without, however, bringing these contacts into engagement. At the end of interval f, the cam O disengages the contact 0 and the latter springs with a snap action into engagement with the contact 0 At the end of interval g, cam O disengages the contact 0 and the latter springs out of engagement with contact 0 Thus contacts 0 and O remainin engagement only for the predetermined limited interval 9.

The oil valve. energizing circuit is traced from conductor 3, which remains energized as before from supply line L through the bottom spring contact 0 the snap contacts 0 and thence directly through the energizing winding of the valve operating electromagnet l8 to the supply line L The electromagnet I 8 immediately operates the oil valve I1 to admit oil under pressure through the atomizing nozzle ll into the combustion chamber l3. Under normal conditions the atomized oil is immediately ignited by the spark between the ignition electrodes l2 thus establishing combustion in the boiler;

The flame detector It at once responds to the presence of combustion and starts to operate its control contact from the cold side to the hot Upon the initial movement of the flame detector contact from the cold side, the energizing circuit of relay C is interrupted. Thereupon, contact C opens and contact 0* is reclosed.

Upon reclosure of contact C the holding circuit for the oil valve operating electromagnet I 8 is'reestablished through the circuits previously traced. The reestablishment of the holding circuit for the oil valve operating electromagnet l8 provides an additional period for maintaining the oil valve open simultaneously with operation of the other elements of the oil burner mechanism after the limited combustion establishing period provided by the closure of cam contacts 0 O and the reopening thereof. These contacts are opened by operation of the cam 0* to move the lower contacts 0 away from the upper contacts 0 at the end of the predetermined limited combustion establishing period 9'. In this way the oil valve is maintained open while the contactor of the flamedetctor I4 is moving from the cold side to the hot side as the flame detectorcontinues to progressively respond to the presence of combustion in the combustion chamber l3. However, the movable contacts of the flame detector must reach the hot side before the expiration of the additional interval h during which the B cam contact is maintained closed. Since the flame detector H is of the quick acting type, it is able under normal operating conditions to move from the cold side during theinterval a and reach the hot side before the end of the additional interval h.

As soon as the movable contact of the flame detector ll reaches the hot side, an entirely new and independent energizing circuit for relay B is established. Thiscircuit is traced from conductor .3 which remains energized as before through the movable contacts of the flame detector in the hot position, conductor ll, 'the contacts B which are closed upon initial closure of the relay B and the operating winding of relay B to the supply line L The independent energizing circuit for the relay B just traced serves to insure continued operation of the oil burner motor and the oil valve opening independently.

This establishment of the independent energizing circuit for the relay B through the hot side of the flame detector contacts as just traced serve to continue operation of the oil burner motor with the oil valve opened independently of further operation of the timing control mechanism as long as combustion is maintained in the combustion chamber l3 and contact A remains closed. However, the timing control motor 42 continues to operate during the interval 2 at the end of which the ignition cam contact is open to deenergize the .ignition transformer and at the end of the final interval 7' the cam contacts T open to deenergize the operating winding of the timing motor 42 with the timing shaft 4| and all of the timing cams thereon returned to the initial start position.

Upon operation of the oil burner long enough to cause the boiler III to supply sufficient heat to the room heating radiator system to satisfy the room thermostat 30, the room thermostat operates to close on contact S and stop further operation of the oil burner. Upon closure on contact S the operating winding of relay A is short circuited and thereby deenergized. Thereupon the contacts A A are open. Upon opening of contact A conductor 3 is disconnected from the supply line L and all elements of the oil burner mechanism and control are deenergized. At the same time, the opening of contact A discon nects the relay winding A from the mid terminal R of the control transformer CT. The flame detector l4 quickly returns its movable contact IE to the cold position in response to the absence of combustion in the combustion chamber l3. Thus the oil burner and control mechanism is in its initial condition ready for a new start whenever the room thermostat again closes on contact R to run the oil humor.

The boiler water temperature thermostat 3| functions to mechanically close the contact A whenever the boiler water temperature falls below a predetermined value.- At the same time the vacuum relief valve 31 is opened by thermostat 3|. Exactly the same sequence of the starting control operations are accomplished upon mechanical closure of the contact A as previously described when A was closed by encrgizing the operating winding of the relay A under the control of the room thermostat 30. In this case the boiler water thermostat 3| mechanically opens the contacts A when the operation of the oil burner has been continued long enough to raisethe boiler water temperature to the value at which the thermostat 3| is set to operate. As previously pointed out, water thermostat 3| permits the oil burner boiler to be operated in the summer time to supply all domestic hot water heating requirements under the control of the boiler water temperature thermostat 3|. However, at any time, winter or summer, that the room temperature falls below the value at which the room thermostat is set to close the contacts R, the oil burner will automatically operate to supply heat to the house heating radiator system. The operation of the vacuum relief valve 31 by the boiler water temperature thermostat 3| effectively prevents a supply of heat in a vapor water storage tank instead of nected from the source of power by means of a suitable disconnecting switch (not shown). This deenergizes all of the oil burner operating and control apparatus. During such a shutdown interval, ambient temperature changes may occur in combustion chamber it such that the contact i5 of the flame detector ii may be moved from the cold position. Consequently, upon reenergizing lines L L relay C will remain deenergized and hence prevent starting the cycle of operation of the burner to establish combustion. In order to permit energization of relay C independently of the position of the flame detector contact i5, an auxiliary switch M is provided for shunting the cold contact of the flame detector it. Thus upon closure of switch M relay C is energized and the normal cycle of operation previously described up to the end of interval g is accomplished. However, in case the switch M is maintained closed after the end of interval y, it will be impossible for the flame detector Ii to effect deenergization of the relay C so as to return the contact (I to the closed position and establish a holding circuit for the oil valve in the manner previously pointed out in case flame is established. Hence the oil valve holding circuit will remain open and the oil valve will close at the end of interval g. This cuts ofi the supply of oil and stops combustion in the furnace. However, upon release of the'switch M after the interval g, the oil burner control mechanism will start a new cycle under normal conditions so that the next time combustion is established during the interval g, the flame detector it is capable of operating to deenergize the relay C and thus maintains combustion established thereafter.

.The switch M preferably is biased to the open position by means of a spring or other suitable means so that it cannot be left permanently in the closed position.

The improved control system and apparatus of the present invention automatically protects against the following changes or abnormal conditions.

If the oil fails to ignite during the limited period 9 during which theoil valve is opened by operation of the cams O the flame detector contact will not leave the cold position and the oil valve will reclose at the end of period 9. The oil burner motor 2i will continue to run until disconnected by opening of cam contact B at the end of interval 72. which in turn opens the contact B The operation of the timing motor 62 continues to complete its cycle. In so doing the arm 80 whichis carried by the cam shaft ti engages with the upper tooth of the lockout ratchet member ti to lift this member one notch. As long as the B relay remains energized due to the flame detector remaining in the cold position,

the spring latch 82serves to engage the first notch on the ratchet member 8i and maintain it in the advance position. As long as the contact A is maintained closed by either the room thermostat or by the water thermostat ii, the

- thereby deenergize all of the equipment.

cam motor 42 continues to operate and start a new cycle. If flame again fails to be established during the limited interval 9, the arm 80 engages the' next tooth on the lockout ratchet 8i and advances this member another notch. Upon completion of the third cycle, the lookout ratchet 8| is advanced to bring the finger it into engagement with the arm 8i extending from the conthe energizing circuit for the timing motor M as previously traced is interrupted and the oil burner mechanism is rendered inoperative until the dimculty causing the failure of establishment of combustion. is corrected.

In case combustion is established during either the second or the third attempt, the fiameJdetector i i moves from the cold position and thereby deenergizes the relay C. This disengages the tact C so as to open this'contact. Thereupon locking pawl 82 from the ratchet member ti and permits the latter to return to its initial position.

It is evident that the lockout ratchet mechanism 1 may be reset at anytime by interrupting the main power circuit L L Whenever the boiler pressure exceeds the value at which the pressure responsive device it is set to open the limit contact L, the conductor 3 is disconnected from supply line L thus deenergizing all parts of the oil-bumer mechanism and control. When normal boiler pressure conditions are restored, a new starting cycle will begin whenever the room thermostat it or water thermostat 3i calls for heat.

Should the boiler water level fall below a predetermined value, the contacts of the low water cutoff device it will be operated to disconnect the conductor i from the supply line L and As more clearly shown in Fig. 5, the low water cutoff mechanism consists of a tube '90 which is mounted in a suitable opening provided in the side of the boiler ill at the minimum safe low water level line. The tube to has a post of heat conducting material ti mounted in the end thereof immersed inthe boiler. A bimetallic thermostatic element 92 is mounted at the free end of the post and extends into latching relation with the cutout switch it. As shown in Fig. 6, the switch 93 is pivotally mounted on the post it and carries the movable bridging contact 95 which is normally maintained in engagement with the cooperating stationary contacts 96. The switch it is normally biased to the open position by the-springs 9i. 1

Surrounding the post @i is the electrical heater winding it which is provided with the two terminal connections iti so that it may be con-' nected in the holding circuit of the .oil valve 'operating electromagnet it as indicated in Fig. 1. This connection of the low water cutout heater in the holding circuit of the oil valve operating electromagnet not only reduces the current therein but effectively insures that in case the heater should accidentally happen to bum'out or fail,

it will prevent maintaining the oil valve open to supply fuel into the furnace combustion cham- .ber. Thus upon any failure or. the low water thermostatic element 92 below the value at which the switch contact 93 is released. However, as soon as the boiler water level falls below that of the tube 90, the heat accumulates in the post.

SI and is transmitted to the thermal element 92 to raise the temperature or the latter. At a predetermined temperature the free end of the thermal element 92 is moved to disengage the switch member 93 and permits the spring 9! to operate the bridging contact 95 to the open position; This disconnects all of the oil burner mechanism and control apparatus from the supply line L as indicated in Fig. i.

In a normal starting cycle, it combustion should be established at any time before the interval g, as might occur due to a leaky oil valve, protection against continued operation of the oil burner mechanism is obtained as follows:

As soon as flame appears in the combustion chamber it, the flame detector moves its contact from the cold side, thus deenergizing relay 0. Thereupon contact C is opened which in turn causes the timing motor 42 to be deenergized. The opening of contact 0 also deenergizes relay B, thus allowing contact B to open and stop operation of the oil burner motor in. As a result combustion is extinguished and the flame detector it again moves its contact to the cold side. Thereupon relays C and B are again energized and the starting cycle is resumed at the point of interruption. If this occurs before cam contact S has opened, the process of momentarily establishing flame and operation of the flame detector to stop the oil burner mechanism in the manner just described will be repeated and the cycle will again be interrupted. However, as soon as the cam contact S has opened, as will eventually happen if it is not open at the first occurrence of premature combustion, the oil burner motor 2| will not start since the starting winding is disconnected. This permits the timing motor 432 to continue the timing cycle without the oil burner motor operating. Continuation of the cycle will advance the lookout ratchet mechanism one notch. During the second cycle flame detection due to 'a leaky oil valve will again cause an interruption of the cycle but will not reset the lookout mechanism because the second tooth oi the lockout ratchet member M is in engagement with the actuating arm til. The second cycle is completed in the same way as in the first. In case the oil valve has cleared itself of the dirt or other obstruction causing leaking during the second or third cycle, premature combustion prior to the interval g will not be obtained and the normal starting sequence will result. However, in case the oil valve continues to leak thecontrol will automatically lock out after three unsuccessful cycles. In the normal starting cycle, the lockout ratchet member ti is reset by deenergization of relay 0 only during the oil valve opening period a when the flame detector leaves the cold contact.

Beginning a starting cycle before the flame detector contact has reset to the cold side is prevented since the cam motor cannot start until contact C closes and contact C cannot close unless the flame detector is in the cold position.

If the starting cycle is interrupted by either voltage failure or by a change in setting of the water thermostat or room thermostat, the starting cycle will be successfully resumed at the point of interruption unless the interruption occurs after the cam contact F has opened. vIn this latter case a complete new starting cycle will follow the completion of the interrupted cycle.

While I have illustrated and described the improvements of the present invention embodied in a control adapted for steam or vapor oil fired boiler, it will be evident that substantially the same control may be applied to a hot water boiler. The only variations are that the low water cutoil" is omitted and the pressure limit control 35 is replaced by a boiler water temperature limit control which functions to open the limit switch L in case the boiler water temperature reaches a dangerous value. In hot water systems, the heater of the low water cutoff device is replaced by a similar resistor which prevents reopening of the oil valve with the holding circuit energized upon a momentary voltage failure.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. In combination, a boiler having an electric motor operated oil burner for heating the water therein, control means for the burner motor including an electro-responsive switch connected to open and close an energizing circuit for the burner motor and having a separate energizing circuit, a thermostatic switch for controlling the separate energizing circuit of said switch to start and stop operation of the burner motor in accordance with predetermined temperature conditions, and means responsive to boiler conditions connected for mechanically operating said switch to start and stop operation of the burner motor only when the separate energizing circuit of said switch is opened under the control of said thermostatic switch.

2. In combination, a boiler having an electric motor operated oil burner for heating the water therein, a temperature responsive device mounted on the boiler to be responsive to the temperature of the water therein, and control means for the burner motor including an electromagnetically operated switch mounted to be operated mechanically by said temperature responsive device, and separate thermostatic means for controlling the encrgizing circuit of said switch to operate the switch independently of said device.

JOHN EATON. 

